body{text-align:center;}
body{width: 1000px;height: 100%; margin: 0 auto; background: powderblue;}
a{text-decoration:none}  
#nav{ width:100%; height:60px; background:skyblue;margin:0 auto} 
#nav li{display:inline; height:60px} 
#nav li a{text-decoration:none;display:inline-block; padding:0 20px; height:60px; line-height:60px; color:white; font-size:16px} 
#nav li a:hover{background:steelblue;} 
#footer{margin-top: 500px;}